1. Technical Field
The present invention refers to an internally threaded, lockable precision nut.
2. State of the Art
It has been previously known to lock nuts on threaded shafts by means of lock screws, and it is also known to arrange lock screws in the nut itself. One example is shown in U.S. Pat. No. 2,520,122, according to which a hole is bored in the wall of the nut from the inside of the nut. Another variant is shown in U.S. Pat. No. 4,227,560, in which the lock nut is provided with a thread bored at an acute angle and intersecting the threaded axial through-hole of the nut. Into this hole a lock screw is inserted and a lock plug is situated at the inner end of the screw, acting against the outer thread of the shaft, which plug is displaced by the lock screw to a locking position. A drawback of this construction is that the locking force acts against only one thread flank with high surface pressure, whereby there is a risk of a permanent impression being produced in the thread. Also, the axial pressure component presses the nut axially as far as the thread play permits, and the result will be unwanted axial throw, which is difficult to balance with remaining locking screws. The accessibility will be inferior due to the acute angle of the lock aperture, etc.
A similar construction, but with axial holes for a lock screw and a lock plug, is also known, but a common drawback of similar designs is that they become expensive.
A common drawback of these and other known designs with plug lock is that the construction does not give efficient clamping, which prevents bearing play, in particular efficient clamping is not achieved after repeated use of the nut.
It has also been proposed (see U.S. Pat. No. 4,086,946 and GB 2 177 178A) to form one or more axial recesses in the nut at a location spaced radially outwardly of the centre hole. A portion of the nut disposed between the recess and the centre hole is resiliently displaceable by applying a radially inward force thereto. Such a force is applied by means of radial lock screws which are threadedly mounted in radial holes formed in the nut. When the resiliently displaceable portion is displaced inwardly, it firmly grips the externally threaded shaft on which the nut is mounted. Such a structure distributes the locking forces more uniformly to prevent the formation of permanent depressions in the externally threaded shaft, and also applies generally axially balanced forces from the nut to the externally threaded shaft. However, shortcomings of such a structure are that the presence of the axial recess decreases the strength and durability of the nut, and that a nut possessing such a recess is relatively difficult and expensive to produce. Also, if a locking fluid (such as an adhesive) were to be introduced into the hole in which the locking screw is disposed, in order to resist unlocking the screw by vibrations, etc., such fluid could flow through the recess and into the thread interface between the nut and the externally threaded member, thereby fouling that thread interface.
Accordingly, it would be desirable to provide a strong, durable lock nut of the type employing a locking screw, which can be easily and inexpensively manufactured and which can receive a locking fluid without fouling the thread interface between the nut and the externally threaded member. Also, there should be provided an emergency locking of the lock nut in case the locking screws, intentionally or unintentionally, are removed. Further, such a lock nut should not result in any permanent impression being formed in the externally threaded member, and it should be possible to axially balance the locking force applied to the nut.